1) Field of the Invention
The present invention relates to novel compounds which are useful as chromogenic compounds in recording materials such as pressure-sensitive and heat-sensitive recording materials, to a preparation process of these compounds, and to recording materials comprising these compound.
2) Description of the Prior Art
A color reaction between a colorless or pale colored electron donative compound (chromogenic compound) and an organic or inorganic electron acceptor (developer) has conventionally been utilized for pressure-sensitive recording, heat-sensitive recording and electroheat-sensitive recording as systems for recording transfered information through the mediation of external energy such as pressure, heat or electricity.
In these systems, fluoran compounds have widely been used as the chromogenic compound.
Many fluoran compounds are known in the prior art, for example, those having the formulas (A), (B), (C) and (D). ##STR2##
However, the compound of the formula (A) has the disadvantage of very low solubility in capsule oil when the compound is used in a pressure-sensitive recording material. Additionally, in the case of applying to a heat-sensitive recording material, the compound colors gray to dark gray when mixed with a developer such as bisphenol A and has the defect of providing only a gray to dark gray colored (soiled) paper by applying the compound to a paper.
The coloring temperature of the compound of the formula (B) is too high to permit its use in a heat-sensitive recording material. Consequently, the performance of these prior art compounds cannot fully meet the present market demand for more rapid and higher density recording. Therefor, a chromogenic compound capable of quickly developing color at a lower temperature has been strongly desired.
Further, the compounds of the formulas (C) and (D) have caused serious disadvantage as the heat-sensitive recording material in practical use. For example, the heat-sensitive recording paper prepared by using these compounds has poor stability such as light stability and moisture resistance in preservation.